Stellar activity cycles as revealed by long-term beat-like patterns from light curves of Kepler

Abstract

Stellar activity cycles have been found on many stars through different methods. Although in debate, an empirical relation has been found where a period of stellar activity cycle Pcyc is positively correlated with rotation period Prot along some segregated branches. In this work, we built a systematic process to search for the Kepler objects that are analogous to the long-term solar brightness variations and investigate their possible origins. After a rigorous selection, we obtained 43 objects that all exhibit clear long-term beat-like patterns and their variability (amplitude of rotational modulation) periods and rotation periods were derived. Due to the 4-year duration of the Kepler mission, our targets are located in the region where the cycle periods are longer than ∼1 yr and shorter than ∼2.5 yr. However, all of our targets exhibit clear and notable quasi-periodic variations in variability, yet we cannot confirm any linear trends that were predicted by previous research independently. This may suggest that in the Kepler realm of the Pcyc–Prot diagram, these relations would mix with each other or the beat-like patterns may not be related to the stellar cycle unless other evidence is provided.